Stable pemetrexed arginine salt and compositions comprising it

ABSTRACT

The present invention relates to arginine salt of pemetrexed of formula (1), particularly to a stable solid form thereof, and to pharmaceutical compositions comprising such salt.

Pemetrexed is a common name for compoundN-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic acid of formula (1)

The compound has been first disclosed in EP 432677.

Pemetrexed is a pharmaceutically active compound, which is used, i.e.,in the treatment of malignant pleural mesothelioma and non-small celllung cancer.

As pemetrexed of the above formula (1) is a bivalent acid (a diacid)comprising two carboxylic groups, it may form various types of saltswith bases. On the other hand, pemetrexed has basic nitrogens and,accordingly, it may form acid addition salts with various acids. Thecommercially available product, sold, e.g., under the brand name ALIMTAby Eli Lilly, comprises hydrated disodium salt of pemetrexed as theactive substance and is supplied as a sterile lyophilized powder forintravenous infusion available in single-dose vials. The preparation oflyophilized pemetrexed disodium composition is disclosed in U.S. Pat.No. 7,138,521.

U.S. Pat. No. 7,138,521 also describes a stable crystalline heptahydrateform of pemetrexed disodium having a characteristic X-ray diffractionpattern. The patent states that pemetrexed disodium can exist in theform of a heptahydrate which is much more stable than the previouslyknown 2.5 hydrate and shows that the primary advantage of theheptahydrate crystalline form over the 2.5 hydrate crystal form is itsstability and also with respect to formation of related substances. Italso shows that when the heptahydrate is subjected to elevatedtemperatures, low humidity, and/or vacuum, it converts to the 2.5hydrate crystal form by loss of water.

The above patent shows that problems may arise because of conversionsbetween different crystalline forms (actually the above mentioned formsare different hydrates, not polymorphic forms) of pemetrexed whenexposed to elevated temperatures, low humidity, etc. Formulationprocesses may involve a variety of the above mentioned adverseconditions, resulting in a possibility that the stability of the finalproduct may be affected.

Disodium salt of pemetrexed is soluble in water, contrary to thepemetrexed diacid of the above formula (1). Formulating water solublepemetrexed salts, however, has not proven to be an easy task, due to itsstability issues. The infusion solution has to be prepared immediatelybefore use, by dissolving the content of the single-dose vial in waterand diluting the obtained solution with an infusion liquid. Therelatively rapid formation of degradants is the main factor which has,so far, prevented ready-to-use aqueous pemetrexed formulations frombeing commercially available. According to WO 2012/015810, five majordegradants of pemetrexed have been observed. Under acidic conditions,decarboxylation of glutamic acid is observed. Under alkaline conditions,degradation proceeds by side chain amide hydrolysis followed bydeamination. In the presence of oxygen, two oxidative degradants result.

There remains a need for preparing alternate pemetrexed formulationswith sufficient stability. In particular, it would be advantageous tofind alternate pemetrexed salts, which may preferentially exist in anamorphous form to prevent polymorphic transitions, which may occurduring storage and formulation of crystalline forms. It is known thatamorphous forms of active ingredients can be relatively more unstable,when compared with crystalline forms. Thus, finding an alternateamorphous form of pemetrexed with sufficient inherent stability isdesirable as it would break a prejudice against using pemetrexed inamorphous form.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a novel pemetrexed salt, which mayadvantageously exist in an amorphous form and is sufficiently stable forformulation in pharmaceutical formulations, particularly lyophilizedformulations.

In the first aspect, the invention relates to arginine salt ofpemetrexed, in particular to a salt of the formula (2)

In a particular aspect, the arginine salt is in solid form,advantageously in an amorphous form.

In the second aspect, the invention relates to a pharmaceuticalcomposition comprising arginine salt of pemetrexed and at least onepharmaceutically acceptable excipient. Preferably, the pharmaceuticalcomposition is a solid composition. Yet preferably, the compositioncomprises the arginine salt of pemetrexed in an amorphous form. In aparticular aspect, the pharmaceutical composition is a lyophilizedpowder useful for reconstitution into an infusion solution by aninfusion liquid.

In a third aspect, the invention relates to a process for makingarginine salt of pemetrexed comprising combining pemetrexed diacid offormula (1) with L-arginine in a solution and removing the solvent. In aparticular aspect, the removal of the solvent is carried out byevaporation or lyophilization.

In a fourth aspect, the invention relates to a process for making apharmaceutical composition, advantageously a solid pharmaceuticalcomposition, comprising a step of combining arginine salt of pemetrexedwith at least one pharmaceutically acceptable excipient. In a particularaspect, the combining step comprises providing the arginine salt ofpemetrexed, contacting it with excipient(s) in a solvent and removingthe solvent. In yet another particular aspect, the step of providing thearginine salt of pemetrexed comprises mixing pemetrexed diacid witharginine in a solvent.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to arginine salt of pemetrexed,particularly to a stable solid form thereof, and to pharmaceuticalcompositions comprising such salt.

The in-house study of possibilities of making various salts ofpemetrexed has revealed that it is difficult to prepare solid stateforms of salts of pemetrexed with various amines. Instead, oily productsare often formed. It was, however, found with surprise that pemetrexedof formula (1) may be combined with basic amino-acids, particularly withL-arginine of formula (3)

(Hereinafter only: arginine) to form a stable solid compound.Advantageously, the molar ratio between pemetrexed and arginine moietiesin the compound is 1:1 or 1:2. A compound having 1:2 molar ratio betweenboth moieties is the preferred compound and it is believed that theproduct comprising the moieties in the above ratio is bis-arginine saltof pemetrexed of the formula (2) above.

Regardless of the actual structure, the compound of the presentinvention defined above and preparable by the process shown below isdenominated throughout the invention as “arginine salt of pemetrexed”.

The solid compound of the above formula (2) may exist in a crystallineform or in an amorphous form, whereby the amorphous form is consideredadvantageous for pharmaceutical applications. The compound is soluble inwater at ambient conditions, wherein the solutions thereof are pHneutral and thus suitable for pharmaceutical applications. The compoundis also sufficiently stable in solid, particularly amorphous, state,both in its isolated form and, as well, in solid pharmaceuticalcompositions. The term “stable” relates to both chemical and physicalstability.

Arginine salt of pemetrexed of the present invention may be prepared bycombining pemetrexed diacid with L-arginine in a pre-defined ratio.L-arginine is a naturally occurring aminoacid, which is commerciallyavailable.

Pemetrexed diacid of the above formula (1) and its preparation isbelieved to have been described for the first time in U.S. Pat. No.5,344,932.

Formation and isolation of pemetrexed diacid from a mixture of water andethanol having a pH of 2.5-3.5 is disclosed in U.S. Pat. No. 7,138,521.Formation and isolation of pemetrexed diacid from an aqueous solutionhaving a pH of 5 is disclosed in U.S. Pat. No.

5,416,211. Formation and isolation of pemetrexed diacid from an aqueoussolution having a pH of 2.8-3.1 is disclosed in U.S. Pat. No. 6,262,262.

Various crystalline forms of pemetrexed diacid as well as methods forobtaining them have been disclosed in U.S. Pat. No. 8,088,919, EP2351755 and EP 2129674. Highly pure pemetrexed diacid may be obtainedaccording to a process disclosed in WO2008/021410A2.

The formation of arginine salt of pemetrexed according to variousembodiments of the present invention is carried out by combiningpemetrexed diacid with arginine in a solution and removing the solvent.The solvent is typically water or a mixture of water with a watersoluble organic cosolvent. Advantageously, the water soluble organiccosolvent has boiling point lower than 100° C. In an example, thesuitable organic cosolvent may be aliphatic alcohol such as methanol,ethanol or isopropanol, aliphatic ketone such as acetone, cyclic ethersuch as dioxan or tetrahydrofuran, aliphatic nitrile such asacetonitrile etc., and mixtures thereof. The organic cosolvent, ifpresent, is typically added after a solution of arginine salt ofpemetrexed in water is obtained.

Typically, pemetrexed diacid and arginine are combined in 1:1 or 1:2molar ratio or close to this ratio (such as from 1:0.9 to 1:1.1 or from1:1.8 to 1:2.2), wherein the 1:2 molar ratio (in ranges from 1:1.8 to1:2.2 mol/mol) is the preferred one for purpose of pharmaceuticalapplications.

Advantageously, arginine is first dissolved in water and after thatpemetrexed diacid is added to the resulted solution. This results inquicker dissolution of inherently sparingly soluble pemetrexed diacid.Cosolvent, if any, is added afterwards.

The solvent is removed from the mixture by evaporation, advantageouslyat diminished pressure, by spray-drying or by lyophilization. Forpurposes of the latter arrangement, the solvent is advantageously water,without presence of an organic cosolvent.

Typically, solid arginine salt of pemetrexed is obtained by the aboveprocess substantially in an amorphous form. Such form is characterizedin that its XRPD pattern does not exhibit any characteristic diffractionpeak. The term “substantially” means at least about 90% of the amorphousform, which includes at least about 95% or in some embodiments at leastabout 99% of amorphous form.

The solid product may comprise residual water and/or organic solvent.Typically, the product comprises less than 10% of these volatilecomponents.

The solid, particularly amorphous, arginine salt of pemetrexed may becombined in various pharmaceutical compositions. Thus, the presentinvention also comprises a pharmaceutical composition comprising anarginine salt of pemetrexed, advantageously the salt of formula (2), andat least one pharmaceutically acceptable excipient. Preferably, thepharmaceutical composition is a solid composition. Yet preferably, thearginine salt of pemetrexed is formulated in the composition in anamorphous form. The composition may be advantageously formulated intodosage forms for parenteral applications. In a particular aspect, thepharmaceutical composition is formulated as a lyophilized powder usefulfor reconstitution into an infusion solution by an infusion liquid.

The pharmaceutically acceptable excipients for purpose of the presentinvention, particularly those useful for making the lyophilizedpharmaceutical formulations, may include one or more of: diluents orbulking agents including one or more sugars such as dextrose, sucrose,mannose, lactose, trehalose and the like, one or more sugar alcoholssuch as mannitol, xylitol and the like; antibacterial preservatives,including one or more of thiomersal, benzalkonium chloride, benzethoniumchloride, chlorobutanol; pH-adjustors such as hydrochloric acid;antioxidants including ascorbic acid, glutathione, L-cysteine, lipoicacid and the like; buffers including one or more of acetate, citrate,tartrate, phosphate, benzoate, and bicarbonate buffers; chelating agentssuch as disodium edetate; tonicity contributors including one or more ofsodium chloride, potassium chloride, dextrose, mannitol, and lactose.The addition of a sugar or sugar alcohol can improve the stability ofpemetrexed formulations. Thus, a suitable lyophilized pharmaceuticalformulation may comprise pemetrexed arginine salt and at least one sugaror sugar alcohol, advantageously mannitol. In various advantageousembodiments, the sugar or sugar alcohol is present in amounts from 0,1 gto 2 g per 1 g of pemetrexed arginine salt.

The unit dose of the pharmaceutical formulation typically comprises from50 to 1500 mg of pemetrexed, calculated as the diacid form.Advantageously, the unit dose comprises 100mg, 250 mg, 500 mg or 1000 mgof pemetrexed. Thus, in a specific aspect, the invention includes a vialor similar container comprising a dose amount of the composition of theinvention. Any suitable sterile vial or container fit for the sterilestorage of a pharmaceutical such as pemetrexed for extended periods oftime may be used. Suitable containers can be glass vials, polypropyleneor polyethylene vials or other special purpose containers.

A further aspect of the invention includes a kit and/or pharmaceuticalcontainer for holding the pemetrexed-containing compositions describedherein. The kit contains at least one pharmaceutically acceptable vialor container containing one or more doses of the pemetrexed-containingformulations/compositions as well as other pharmaceutically necessarymaterials for storing and/or administering the drug, includinginstructions for storage and use, infusion bag or container with aninfusion diluent etc. The solid pharmaceutical composition comprisingarginine salt of pemetrexed of the present invention can be made by aprocess comprising a step of combining an arginine salt of pemetrexedwith at least one pharmaceutically acceptable excipient. In a particularaspect, the combining step comprises providing the arginine salt ofpemetrexed, e.g. by a process disclosed above, contacting it with theexcipient(s) in a solvent and removing the solvent. In yet anotherparticular aspect, the step of providing the arginine salt of pemetrexedcomprises mixing pemetrexed diacid with L-arginine in a solvent.

The process of making compositions of the present invention typicallycomprises a step of weighing the respective ingredients and dissolvingthem in water, preferably under stirring. Thus, in one embodiment,arginine salt of pemetrexed and at least one excipient listed above areweighed and dissolved in water. In an alternate embodiment, the argininesalt of pemetrexed is prepared in situ by combining pemetrexed free acidwith arginine in the desired molar ratio, which typically is 1:1 or 1:2molar ratio or close to this ratio, wherein the 1:2 ratio (in rangesfrom 1:1.8 to 1:2.2 mol/mol) is the preferred one.

Advantageously, water is first deoxygenated by a suitable technique,e.g. by saturating it by an inert gas, by deaerating with ultrasoundetc.

The dissolution process is preferably conducted in atmosphere of aninert gas such as nitrogen or argon.

In the last stage, pH of the composition is adjusted to the desiredvalue by an acid or base. The obtained solution is filtered andsterilized and filled into vials comprising the desired amount ofpemetrexed per vial.

The arginine salt of pemetrexed is typically present in the solutions inconcentrations between 10 and 60 mg/ml, preferably between 15 and 50mg/ml, when calculated as anhydrous pemetrexed. In alternative aspects,the amount of pemetrexed may be outside these ranges but the amountswill be sufficient for single or multiple administrations of dosagesgenerally regarded as effective amounts.

Water must be of pharmaceutically acceptable quality. Typically, waterin quality “for injections”, as defined in acknowledged Pharmacopoeias,is used. In an advantageous aspect, water is the only liquid componentpresent in the compositions. In an advantageous embodiment of theinvention, the adjusted pH value of the solution is from about 6.5 toabout 8.5. The suitable pH adjustor may be any suitable pharmaceuticallyacceptable acid, base, salt or a combination thereof.

In the next step, the solvent, typically water, is removed from thecomposition. Typically, water is removed by lyophilization(freeze-drying) under suitable conditions. Freeze drying can beconducted at temperatures from about −10 to about −60° C., under vacuumin the range of about 0.5 to about 100 Pa.

In an advantageous embodiment, the subject of the lyophilization processis the content of vials prepared as shown above. Accordingly, thelyophilization process yields a composition comprising the unit dose ofpemetrexed, which typically comprises from 50 to 1500 mg of pemetrexed,calculated as the diacid form.

In the last step of the overall process, the vials are closed by asuitable stopper, labeled and packed into suitable container.

The compositions and formulations of the present invention areparticularly suited for parenteral administration. For suchadministration, the composition is reconstituted prior to its use by anappropriate liquid medium. The medium may include sterile water, a pHbuffered solution, sodium chloride solution, a dextrose solution orcombination of the same.

The compositions of the present invention may be used in medicine,particularly for treating a pemetrexed sensitive disease in mammals.Thus, in yet another aspect of the invention, there are provided methodsof treating a pemetrexed sensitive disease in mammals. Pemetrexedsensitive diseases include, but are not limited to, cancers, such asmalignant pleural mesothelioma and non-small cell lung cancer. The useor methods include administering an effective amount of a pemetrexed-containing composition as described herein to a mammal in need thereof.

The following examples illustrate the invention.

EXAMPLES Example 1

To 500 mg of pemetrexed diacid and 407 mg of arginine, 6 ml of water wasadded. The mixture was stirred until a clear solution was formed. Thistook approximately 5 minutes. The solvent was evaporated and the residuewas dried over night at 40° C. under vacuum.

XRPD test confirmed amorphous character of the product.

TGA curve exhibits gradual mass loss of 4.738% of water between 25 and220° C.

NMR confirmed the structure of bis-arginine salt (formula (2))

Example 2

1000 mg of pemetrexed (diacid) and 815 mg of arginine was added to 6 mlof water. The mixture was stirred at ambient temperature until a clearsolution was formed.

The solution was divided into 6 fractions and the following cosolventswere added to the respective fractions:

.01 3 ml of methanol

.02 3 ml of ethanol

.03 2 ml of isopropanol

.04 2 ml of acetonitrile

.05 2 ml of tetrahydrofuran

.06 2 ml of acetone

The solutions were evaporated on a rotary vacuum evaporator. The solidresidues were dried at 40° C. under vacuum over night.

Analysis of the material by XRPD has proven an amorphous material.

Example 3

Process for making unit dose lyophilized composition (50 mg pemetrexedper vial):

Under inert atmosphere of nitrogen, 875.0 mg of pemetrexed (diacid) wasdissolved in a solution of 731.0 mg arginine (2.1 molar equivalentsrelated to pemetrexed) in 30 ml of Water for injections under stirring.After that, 875 mg of mannitol was added and dissolved. The pH wasadjusted to about 7.5 by 1 M hydrochloric acid and the weight of thesolution was adjusted to 35 gram amount by Water for injections. Thesolution was filtered through PVDF filter 0.2 microns, filled in clear10 R vials per 2 grams and freeze dried according to the programpresented in the table.

Duration Temperature Vacuum Safety Pressure Process Phase (hh:mm) (° C.)(mbar) (mbar) Loading 00:00 +5 Fast freezing 01:00 −45 Freezing 01:30−45 Freezing 00:45 −15 Annealing 01:00 −15 Freezing 01:30 −45 Freezing02:00 −45 Evacuation 1 00:10 −45 0.37 0.63 Sublimation 05:00 +5 0.370.63 Sublimation 06:15 +5 0.37 0.63 Evacuation 2 00:10 +5 0.06 0.63Second drying 05:35 +30 0.06 0.63 Second drying 03:30 +30 0.06 0.63

A stability study has been performed in order to compare the compositionof the present example with the commercial product ALIMTA 100 mg and 500mg. Impurities present in the pemetrexed-comprising formulations duringstability studies performed were detected by high performance liquidchromatography (HPLC) equipped with UV detector at a suitable wavelength(typically 227 nm) and calculated on a normalized peak area response(“PAR”) basis. As an acceptable limit, demonstrating sufficientstability at the corresponding sampling point, the sum of peaks of allindividual degradants in the inventive compositions should not exceed 2%of the total PAR. The peak size of any individual degradant should notexceed 1% of the total PAR. In the tables below, the “UN” denotes anunknown impurity, Impurities A, B, C and D have known structure(Ph.Eur.).

The Originator product Alimta was analyzed in the beginning (ZERO time)and after storage at various conditions.

Alimta 500 mg, Batch A721520E

3 months 6 months 2 weeks 40° C./ 40° C./ Name RRT Zero 50° C. 75% RH75% RH UN 0.33 nd nd nd 0.01 UN 0.37 0.04 0.04 0.05 0.04 UN 0.39 nd nd0.01 nd UN 0.46 0.15 0.14 0.13 0.14 Impurity A 0.58 0.04 0.04 0.04 0.04Impurity B and C 0.66 0.11 0.11 0.08 0.09 UN 0.74 0.01 0.01 0.01 0.01 UN0.88 0.01 nd 0.01 0.02 UN 0.91 0.01 0.01 0.01 0.01 UN 1.78 nd 0.01 0.010.01 ΣIMP (% IN) 0.37 0.36 0.35 0.37

Alimta 100 mg, Batch A693326

1 month 6 months 2 weeks 40° C./ 40° C./ Name RRT Zero 50° C. 75% RH 75%RH UN 0.34 0.02 nd nd nd UN 0.41 0.01 0.01 0.01 nd UN 0.48 0.06 0.050.01 nd UN 0.50 nd nd 0.02 0.05 Impurity A 0.64 0.03 0.03 0.03 0.03Impurity B and C 0.72 0.04 0.04 0.03 0.03 UN 0.81 0.02 0.02 0.02 0.02 UN0.94 0.01 nd nd nd UN 0.96 0.01 0.01 nd 0.01 UN 0.99 0.02 0.01 0.01 0.01UN 2.01 nd nd nd 0.01 ΣIMP (% IN) 0.22 0.17 0.13 0.16

Pemetrexed. Arg 2 salt stability (Composition of Example 3)

1 month 2 weeks 40° C./ Name RRT ZERO 50° C. 75% RH Pemetrexed (% in)1.00 99.71 99.69 99.69 L-arginine 0.07 0.05 0.05 0.05 imp_A 0.78 0.040.04 0.04 imp_D 0.91 <0.04% <0.04% <0.04% UN 0.92 0.10 0.08 0.08 imp_B0.96 <0.04% <0.04% <0.04% imp_C 0.98 <0.04% <0.04% <0.04% ΣIMP (≧0.04%IN) 0.19 0.17 0.17 ΣIMP (<0.04% IN) 0.10 0.14 0.14 ΣIMP (% IN) 0.29 0.310.31

Result: pemetrexed-arginine salt in lyophilized composition is fullycomparable to commercial pemetrexed disodium composition from stabilitypoint of view.

1. Arginine salt of pemetrexed of formula (1)


2. The salt according to claim 1 having the formula (2)


3. The salt according to claim 1 in solid form.
 4. The salt according toclaim 3, in amorphous form.
 5. A pharmaceutical composition comprisingthe arginine salt of pemetrexed according to claim 1 and at least onepharmaceutically acceptable excipient.
 6. The composition according toclaim 5, which is a solid composition.
 7. The composition according toclaim 6 comprising the arginine salt of pemetrexed in an amorphous form.8. The composition according to claim 1, which is a lyophilized powderuseful for reconstitution into an infusion solution by an infusionliquid.
 9. The composition according to claim 1, wherein the excipientinclude one or more of diluents or bulking agents including one or moresugars such as dextrose, sucrose, mannose, lactose, trehalose and thelike, one or more sugar alcohols such as mannitol, xylitol and the like;antibacterial preservatives, including one or more of thiomersal,benzalkonium chloride, benzethonium chloride, chlorobutanol;antioxidants including ascorbic acid, glutathione, L-cysteine, lipoicacid and the like; pH-adjustors such as hydrochloric acid; buffersincluding one or more of acetate, citrate, tartrate, phosphate,benzoate, and bicarbonate buffers; chelating agents such as disodiumedetate; tonicity contributors including one or more of sodium chloride,potassium chloride, dextrose, mannitol, and lactose.
 10. The compositionaccording to claim 8, wherein the excipient is mannitol.
 11. A processfor making arginine salt of pemetrexed comprising combining pemetrexeddiacid of formula (1) with L-arginine in a solution and removing thesolvent.
 12. The process according to claim 11, wherein the removal ofthe solvent is carried out by evaporation or lyophilization.
 13. Aprocess for making a pharmaceutical composition, comprising a step ofcombining arginine salt of pemetrexed with at least one pharmaceuticallyacceptable excipient.
 14. The process according to claim 13, wherein thepharmaceutical composition is a solid composition.
 15. The processaccording to claim 13, wherein the step of combining comprises providingarginine salt of pemetrexed, contacting it with excipient(s) in asolvent and removing the solvent.
 16. The process according to claim 15,wherein the step of providing the arginine salt of pemetrexed comprisesmixing pemetrexed diacid with arginine in a solvent.